1. Field of the Invention
This invention relates to a manufacturing method of a semiconductor device using a wiring base material having conductor wiring on an insulating film as an electric path from a semiconductor element to the outside and the semiconductor device provided by sealing with a resin shows excellent resistance to cracks of soldering on the printed circuit board.
2. Description of the Related Art
A tape carrier type semiconductor device or a tape ball grid array type semiconductor device is known as a semiconductor device using a wiring base material having conductor wiring on an insulating film as an electric path from a semiconductor element to the outside. Further, a semiconductor device comprising a metal radiator plate brought into contact with a semiconductor element of a tape carrier type semiconductor device is also known.
FIG. 4 shows an example of the tape carrier type semiconductor device. An electrode of a semiconductor element 1' is connected with a wiring conductor 22' of a wiring base material 2' having an opening 20' by a bump method to provide a semiconductor element with a wiring base material (in FIG. 4, numeral 21' is an insulating film). Further, an electrode face side 11' of the semiconductor element 1' is sealed with a sealing resin material 41' through the opening 20' of the wiring base material 2' by a mold method, etc.
In the resin sealing, the stress acting on the sealing resin material is substantially zero when the resin is melted, namely, the state is stress-free. However, since the heat shrinkage factor of the sealing resin material is extremely large as compared with that of the semiconductor element, as the melted resin is cooled and hardened, namely, the sealing is concluded, a tension stress occurs on a sealing resin layer and finally a residual stress is contained in the sealing resin layer.
FIG. 5 shows the use state (connecting state on the printed circuit board) of the semiconductor device. The wiring conductor 22' of the wiring base material 2' in the semiconductor device is soldered to a conductor 52 formed on a based board 51 of a circuit board 5 by a flow method or a reflow method.
As known, to solder a semiconductor device sealed with a resin, it is feared that the moisture content absorbed to a sealing resin layer during the storage of the semiconductor device may be evaporated by heating at the soldering time and that cracks may occur in the sealing resin layer due to the vapor pressure. This phenomenon occurs because the strength of the sealing resin material heated to the soldering temperature (high-temperature strength) cannot endure the vapor pressure.
However, if the high-temperature strength of the sealing resin material is enhanced to prevent cracks from occurring in the sealing resin layer, the glass transition temperature of the sealing resin material rises accordingly and the moisture absorption percentage rises, leading to an unavoidable rise in the vapor pressure. On the other hand, if the moisture absorption percentage of the sealing resin material is lowered, the glass transition temperature lowers accordingly, resulting in unavoidable degradation of the high-temperature strength of the sealing resin material. Therefore, there is a limit to selection of the sealing resin material itself to prevent crack occurrence in the sealing resin layer caused by heating at the soldering time.
By the way, metal foil demonstrates extremely excellent water blocking property and is generally used as a water blocking layer of a plastic insulator, for example, a plastic power cable covered with a plastic layer to avoid the electric breakdown by absorbed water.
However, to use metal foil as a water blocking layer of the sealing resin layer of the semiconductor device, the following unreasonableness is feared:
It is inevitable that the sealing resin layer of the semiconductor device contains a tension residual stress on a mold thermal stress history as descried above. As heating of the sealing resin layer proceeds, the tension residual stress decreases and goes to a stress-free state with heating at the soldering time. Thus, thermal stress behavior of the sealing resin layer because of heating at the soldering time does not promote crack occurrence in the sealing resin layer caused by the vapor pressure; it is expected to contribute to suppression of crack occurrence.
However, assuming a structure having metal foil with zero stress or in a residual stress state not related to the residual stress laminated integrally on the sealing resin layer 41' of the semiconductor device in FIG. 4, namely, the sealing resin layer 41' in an internal dynamical state in which a tension stress caused by a mold thermal stress history remains, but decreases because of heating of soldering, the metal foil hinders the sealing resin layer from going to a stress-free state because of heating at the soldering time, resulting in a thermal stress occurring in the sealing resin layer. This thermal stress is superimposed on the stress with the vapor pressure as a load to increase the stress. If the vapor pressure can be decreased by decreasing moisture absorption due to the water blocking function of the metal foil, it is feared that the crack prevention effect in the sealing resin layer may be degraded as compared with the case where the stress increase caused by the superimposing does not occur.